# NB: commit() is responsible for calling tpc_begin() on the storage.
# It uses self._begun to track whether it has been called.  When
# self._begun is None, it has not been called.

# This arrangement allows us to handle the special case of a
# transaction with no modified objects.  It is possible for
# registration to be occur unintentionally and for a persistent
# object to compensate by making itself as unchanged.  When this
# happens, it's possible to commit a transaction with no modified
# objects.

# Since tpc_begin() may raise a ReadOnlyError, don't call it if there
# are no objects.  This avoids spurious (?) errors when working with
# a read-only storage.

Add code to handle this in Connection's tpc_begin() and commit()
methods.

Add two tests in testZODB.

An earlier revision (1.68) fixed invalidation code when an object had
no oid (oid == None).  There is no longer anyway to get None in
_invalidated, and it has been a long time since a None there meant
"invalidate everything."

At long last, then, remove all the code deal with the invalidate
everything behavior.

  invalidations instead of only the ones that hit the cache.

- Support reading gzipped files.  This is triggered automatically when
  the filename ends in .gz.  Also support reading from stdin (pass '-'
  as filename).

- Widen the FLIPS column by one to match the EVICTS column width of
  the LRU simulation.

- Support simulating alternative caching strategies.  For now, only
  LRU is supported, triggered by the -l option.

- Change the Simulation base class to store the cachelimit argument.
  (The constructor signature must be the same across all subclasses.)

the filename ends in .gz.  Also support reading from stdin (pass '-'
as filename).

base class.

report overall statistics for all columns.

ZEO_CACHE_TRACE set (see stats.py for file format description).

correct header sizes.

loads and hits and the hit rate is now reported every 15 minutes.

added DanglingReferenceError. A new exception for storages to report the fact that a transaction is storing a reference to an object that does not exist. Doing this is 'a bad thing', although it is not entirely clear that it is prohibited. So far only DirectoryStorage makes this check. This is given its own exception class because some code may be able to catch it, and regenerate the object that the storage thinks does not exist.

p can be negative, which merely means the offset is in the other file.

p can be negative, which merely means the offset is in the other file.

- Always print start and flip events.  Add the newline before the
  stats back.

records).

Report distribution of "current file" bit.

  trace data; first and last timestamp, and their difference in
  seconds; how many records had their version bit set.

 - All large numbers reported are formatted with commas
   (e.g. '1,234,567').

more.  (ZEO1 will follow after lunch.)

records.  This is much faster (the old code took 16 second to write
120,000 records on my home box, the new code takes about 2.7 seconds).

A new script, stats.py, is provided to analyze statistics.

As suggested by Toby Dickenson.

The ImmediateCommitStrategy storage is not a ZEOStorage, but a FileStorage.

when the connection is closed is called 'close()' when it doesn't
close the manager, but tells the manager that one particular
connection is closed.  Rename it to 'close_conn()'.

The previous code just called tpc_abort() on the server, but that
wouldn't restart any waiting transaction.

- Add some expository comments.

- Add some asserts documenting non-obvious assumptions.

- Make modifiedInVersion a delegated method, since it does nothing
  special.

- Fix a bug in undo(); it was passing a list of triples (oid,None,'')
  to the server.invalidate() call rather than a list of tuples
  (oid,'').  There are no unit tests for undo(), so this was never
  caught.  I guess few people care about undo() now that we have
  transactionalUndo().

- In ImmediateCommitStrategy.store(), only catch exceptions that
  inherit from Exception raised by the storage's store() call; the
  client is only checking for those in the list of serials.

- Remove unused instance variable 'invalidated' from the
  DelayedCommitStrategy class.